UNAUTH RWY ENTRY BY ACR.

Narrative

I TAXIED PARTLY ONTO THE ACTIVE RWY WITHOUT PROPER CLRNC BECAUSE OF AN ERRONEOUS PRECONCEIVED IDEA THAT I HAD BEEN CLRED TO DO SO. HAVING A SHORT TAXI WITH HVY CHKLIST DUTIES CONTRIBUTED TO THE ERROR. WE HAD BEEN GIVEN A CLRNC TO TAXI ON TO RWY 3 AND HOLD SHORT OF THE DEP RWY 30L. THE FO RESPONDED 'CLRED INTO POS 30L.' THE CTLR DID NOT QUESTION OR CORRECT HIS RESPONSE. (FAIRLY BUSY ATC AT THE TIME). THERE WAS AN SMT Z ON SHORT FINAL WHEN WE GOT THE CLRNC. WE PROCEEDED ON TO RWY 3 AND STARTED ON TO 30L WHEN I STOPPED THE ACFT REALIZING WE HAD NOT BEEN OFFICIALLY CLRED INTO POS. WE CALLED READY FOR TKOF. TWR SAID 'HOLD SHORT.' WE SAID 'WE HAD CROSSED THE HOLD LINE; DID HE WANT US TO TAXI ACROSS AND HOLD ON THE OTHER SIDE?' HE SAID 'HOLD YOUR POS;' AND THEN INSTRUCTED SMA Y; ON CLOSE IN L BASE; TO GAR. WE HAD NOT SEEN THAT ACFT BECAUSE HE WAS OUT OF OUR VIEW BEHIND AND TO OR R. I HAD A PICTURE IN MY MIND THAT WE WOULD BE CLRED INTO POS FOR TKOF WHEN ACFT Z ON SHORT FINAL HAD LANDED. WE WERE FAR ENOUGH AWAY WHEN GIVEN OUR CLRNC THAT THE SHORT FINAL ACFT Z WOULD NO LONGER BE A FACTOR WHEN WE ARRIVED AT THE RWY. THE FACT THAT THE CTLR DID NOT CORRECT OUR READBACK OF 'CLRED INTO POS' TENDED TO MODIFY MY PICTURE TO BEING CLRED INTO POS WHEN WE GOT TO THE RWY. WE HAD A RATHER SHORT TAXI FROM OUR GATE TO THE DEP RWY (APPROX 2 MINS) SO WE WERE SOMEWHAT BUSY DOING CHKLIST. I STOPPED WITH JUST THE NOSE PAST THE HOLD LINE. THERE WAS NO OTHER ACFT TAXIING NEARBY AT THE TIME. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO. RPTR GAVE ADDED INFO REF OTHER ACFT INVOLVED AND SEPARATION DISTANCE. SAYS HIS FO WAS NEW TO TYPE ACFT AND HAD JUST MOVED UP FROM FLT ENG TO COPLT. SAYS ACFT Y COULD HAVE SAFELY LANDED. NOT SURE IF THERE ACTUALLY IS A HOLD LINE FOR RWY 30L AT THAT END OF RWY. RPTR DID NOT NOTE DIFFERENCE BTWN ATC CLRNC AND THE FO READBACK; BUT LATER REALIZED THAT THEY WERE NOT CLRED INTO POS AND STOPPED WITH NOSE OF ACFT ABOUT ON RWY EDGE.